EP0540331B1 - Electric field absorption light modulation driving apparatus and method - Google Patents

Electric field absorption light modulation driving apparatus and method Download PDF

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Publication number
EP0540331B1
EP0540331B1 EP92309917A EP92309917A EP0540331B1 EP 0540331 B1 EP0540331 B1 EP 0540331B1 EP 92309917 A EP92309917 A EP 92309917A EP 92309917 A EP92309917 A EP 92309917A EP 0540331 B1 EP0540331 B1 EP 0540331B1
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EP
European Patent Office
Prior art keywords
modulation device
level
voltage
driving signal
light
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EP92309917A
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German (de)
French (fr)
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EP0540331A2 (en
EP0540331A3 (en
Inventor
Masaru c/o FUJITSU LIMITED Onishi
Kazuhiro c/o FUJITSU LIMITED Suzuki
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Fujitsu Ltd
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Fujitsu Ltd
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    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/015—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on semiconductor elements having potential barriers, e.g. having a PN or PIN junction
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/0121—Operation of devices; Circuit arrangements, not otherwise provided for in this subclass
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/015—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on semiconductor elements having potential barriers, e.g. having a PN or PIN junction
    • G02F1/0155—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on semiconductor elements having potential barriers, e.g. having a PN or PIN junction modulating the optical absorption
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/015—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on semiconductor elements having potential barriers, e.g. having a PN or PIN junction
    • G02F1/0155—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on semiconductor elements having potential barriers, e.g. having a PN or PIN junction modulating the optical absorption
    • G02F1/0157—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on semiconductor elements having potential barriers, e.g. having a PN or PIN junction modulating the optical absorption using electro-absorption effects, e.g. Franz-Keldysh [FK] effect or quantum confined stark effect [QCSE]
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F2203/00—Function characteristic
    • G02F2203/19—Function characteristic linearised modulation; reduction of harmonic distortions

Definitions

  • the present invention relates to an electric field absorption light modulation driving apparatus and method.
  • Very fast information transmission and information transmission over a long distance are important objects achieved by a current optical communication system.
  • an external modulation method instead of a direct modulation method, which may cause, for example, charping phenomena occurring in a distributed feedback laser, is required.
  • An electric field absorption light modulation device (this is referred to as "EAM" hereinafter) is one such method fulfilling the requirement.
  • An EAM constructed with an integrated light emission source is expected to bring about miniaturization and high performance in an apparatus relevant to the system.
  • the composition of an EAM driving apparatus of a related art is described below with reference to FIGS.1A through 1C.
  • the EAM driving apparatus comprises a laser diode device (this is referred to as "LD device” hereinafter) 1, a modulation device 2, EAM 3, a reference voltage terminal 4, a bias terminal 5, and a driving terminal 6.
  • the LD device 1 provides a LD device output 7 to the modulation device 2, and the modulation device 2 provides a modulation device output 8.
  • the light transmittance is approximately 100 % when the absolute value of the driving voltage (negative voltage) applied to the terminal 6 is zero (0) (point (C1)), most of light of the LD device output 7 applied to the modulation device 2 passes through modulation device 2, and appears as modulation device output 8 without experiencing significant attenuation.
  • the LD device output 7 begins to be absorbed by the modulation device 2 at the point (C2) wherein the absolute value of the negative driving voltage begins to increase.
  • an electrical driving waveform in the negative driving voltage applied to the modulation device 2
  • an optical output waveform in the modulation device output 8
  • the modulation device output 7 supplied to the modulation device 2 is kept at a constant value.
  • the driving voltage applied to the modulation device 2 fluctuates in a range a delta-V H at the upper voltage (that is, small absolute value of a negative voltage) part of the driving waveform shown FIG.3B. Such fluctuation may occur because of, for example, the high harmonics present in such a pulse wave.
  • the optical output (modulation device output 8) fluctuates in the range delta-P H in the upper part of the optical output waveform shown in FIG.3C.
  • the curve (C) since the inclination of the curve (C) is sharp, the variation of the driving voltage is relatively amplified as a result of being converted into an optical output, in the upper part (C4).
  • signal degradation occurs such as when a slight amount of ringing in an electrical driving waveform results in much noise appearing in the upper part of the optical output. This results in a degradation of parameters such as optical receiver code-error rate and optical waveform.
  • the EAM driving apparatus in the related art has a problem in that it is not possible to utilize the advantages of an optical fiber transmission line sufficiently, which advantages are obtained as a result of its low-loss and wide-frequency-range characteristics.
  • a general object of the present invention is to provide EAM driving apparatus and method wherein the above mentioned problem occurring in the related art is eliminated.
  • a particular object of the present invention is to provide an EAM driving apparatus and method wherein signal fluctuation present in an input information signal does not result in noise in the optical output of the modulation device of the EAM.
  • an electric field absorption light modulation unit comprising a light emission device for emitting light; a modulation device for transmitting the light with a variable transmittance in order to provide modulated light; and driving signal generating means for generating in response to an input information signal a driving signal to be applied to the modulation device, the modulation device varying its light transmittance in response to the driving signal level, characterised in that the driving signal generating means has a level setting means setting the level of a portion of the driving signal in which an undesirable level fluctuation occurs to correspond to a constant working range of the modulation device, the light transmittance of the modulation device having a constant value in the constant working range.
  • an electric field absorption light modulation driving method comprising the steps of (a) causing a light emission device to emit light, (b) causing a modulation device to vary its light transmittance of light applied by the light emission device so as to provide light as a result of modifying thereof; and (c) generating a driving signal from an input information signal and applying the driving signal to the modulation device to vary the light transmittance thereof, in which step (c) provides a portion of the driving signal in which an undesirable level fluctuation occurs in a constant working range of the modulation device, the light transmittance of the modulation device staying at a constant value in the constant working range.
  • said driving signal in a fluctuation range in which an undesirable level fluctuation may be present corresponds to a constant working range of said modulation device, said light transmittance thereof staying at a constant value in said constant working range.
  • the undesirable fluctuation present in the input information signal does not result in any noise appearing at the optical output. Therefore, for a long-distance optical transmission system, for example in an EAM driving apparatus using the above mentioned electric field light absorption modulation driving apparatus or method, it is possible to utilize the advantage of an optical fiber transmission line sufficiently, which advantages are obtained as a result of low-loss and wide-frequency-range characteristics.
  • FIG.4A A principle of an EAM driving apparatus of one embodiment of an electrical field absorption light modulation driving apparatus and method according to the present invention is described below with reference to FIGS.4A through 4D.
  • the configuration shown in FIG.4A resulted from modifying the configuration shown in FIG.1A. That is, an amplifying device 10 and modifying device 11 are added.
  • an amplifying device 10 and modifying device 11 are added.
  • the description of those parts in the configuration in FIG.4A which correspond to the parts in FIG.1A is omitted, and the same numbers as those used for the parts in FIG.1A are given to the corresponding parts in FIG.4A.
  • a predetermined voltage is applied to a terminal 4 of the EAM 3 so that the predetermined voltage is applied to the cathodes of both the LD device 1 and the modulation device 2, and a predetermined electric current I B is supplied to the anode of the LD device 1 via a terminal 5 of the EAM 3 so that the LD device 1 emits a constant light quantity, as shown in FIG.4A.
  • the anode of the modulation device 2 is connected to the output terminal of the modifying device 11 via a terminal 6 of the EAM 3, and the input terminal of the modifying device 11 is connected to the output terminal of the amplifying device.
  • the modifying device 11 or both the amplifying device and the modifying device 11 acts or act as a driving signal generating means.
  • An input information signal (input data as shown in FIG.4D) supplied to the input terminal 9 of the amplifying device 10 is then amplified and inverted in the amplifying device 10.
  • the output signal of the amplifying device 10 is then supplied to the modifying device 11.
  • the modifying device 11 then performs the following operation on the output signal of the device 10.
  • the upper part of the electrical driving waveform (driving voltage, acting as a driving signal) is set to a constant non-zero voltage V H , as shown in FIGS.5A through 5C.
  • the constant voltage V H in the present invention is obtained as a result of shifting the prior art constant voltage V H from zero (0) in a positive direction (left direction in FIGS.5A and 5B).
  • the range between zero (0) voltage and the constant voltage V H is larger than the range obtained as a result of adding a predetermined margin range delta-V M to the range delta-V H of the expected undesirable fluctuation appearing in the H (high) level range (upper part) of the driving voltage as shown in FIGS.5A and 5B.
  • the predetermined margin range delta-V M is determined as the result of consideration of each relevant component used, the range of ambient temperature at which the components are used, and various factors due to aging of the components.
  • the light transmittance of the modulation device 2 is kept at a constant value (in this embodiment, this is 100 %) where a driving voltage is positive, that is, the characteristic curve (C5) has a saturation characteristic.
  • the optical output is kept at a constant value in spite of any undesirable fluctuation being present in the driving voltage, under conditions where the light output applied to the modification device 2, which output is emitted from the LD device 1, is kept at a constant value.
  • the range delta-P H of the level fluctuation in the optical output is zero (0) as shown by FIG.5C even if a range delta-V H of voltage fluctuation is present in the driving voltage as shown in FIG.5B.
  • the voltage fluctuation in a range delta-V H shown in FIG.3B being included in the electrical driving waveform does not result in the degradation shown in FIG.3C of the optical output waveform.
  • the voltage fluctuation in the range delta-V H results from a corresponding level fluctuation being present in the input information signal (input data) supplied to the amplifying device 10.
  • the input information signal input data supplied to the amplifying device 10.
  • FIG.6A shows concrete forms of the amplifying device 10 and modifying device 11 shown in FIG.4A.
  • the terminal 4 of the EAM that is, the cathodes of both the LD device 1 and the modulation device 2 is grounded in this configuration as shown in FIG.6A.
  • a transistor 20 acts to amplify and invert an input data waveform.
  • a diode (being as a second pn junction element) 21 acts to modify the waveform, that is, to shift the level of the waveform, and a load resistor (acting as a load element) acts as load for the transistor 20.
  • the diode 21 acts as a constant voltage providing means.
  • a voltage V G corresponding to an input information signal (input data) is supplied to the gate of the transistor 20, a negative voltage V S is applied to a source of the transistor 20, and a voltage V D at the drain of the transistor 20 is applied to the terminal 6 of the EAM, that is, to the anode of the modulation device 2.
  • the anode of the diode 21 is connected to the terminal 6 of the EAM 3, and a positive first reference voltage V R1 is applied to the cathode (24) of the diode 21.
  • One terminal of the resistor 22 is connected to the terminal 6 of the EAM 3, and a positive second reference voltage V R2 is applied to the other terminal of the resistor 22.
  • the transistor turns “ON” when the level of the input information signal (input data) goes high (H).
  • the output voltage V D of the transistor 20 goes low.
  • the present voltage V D is previously set to a voltage V L which is the negative bias voltage of the EAM 3, that is, which voltage causes the light transmittance of the modulation device 2 to be zero (0) % as shown in FIG.5A.
  • the optical output of the modulation device of the EAM 3 is "OFF", that is, L (low) level shown FIG.6C when the level of the input information signal (input data) is H (high) level shown in FIG.6D.
  • the transistor 20 turns “OFF" when the level of the input information signal (input data) is L (low). Then, the voltage at the anode (6) of the modulation device 2 becomes a constant value which is determined by the first and second reference voltages V R1 and V R2 , characteristics of the diode 21, and the resistance value of the resistor 22.
  • the present constant value is previously set to the above mentioned positive constant voltage V H shown in FIG.5A.
  • the H (high) level range of the driving voltage corresponds to a range of the light transmittance of the modulation device 2, in which range the light transmittance is in a saturated condition.
  • an optical output waveform should not contain noise, that is, the level fluctuation delta-P H appearing in the H (high) level range should be zero (0) as shown in FIG.5C.

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  • Physics & Mathematics (AREA)
  • Nonlinear Science (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Optical Communication System (AREA)
  • Semiconductor Lasers (AREA)

Description

BACKGROUND OF THE INVENTION
The present invention relates to an electric field absorption light modulation driving apparatus and method. Very fast information transmission and information transmission over a long distance are important objects achieved by a current optical communication system. For this purpose, an external modulation method instead of a direct modulation method, which may cause, for example, charping phenomena occurring in a distributed feedback laser, is required. An electric field absorption light modulation device (this is referred to as "EAM" hereinafter) is one such method fulfilling the requirement. An EAM constructed with an integrated light emission source is expected to bring about miniaturization and high performance in an apparatus relevant to the system.
The composition of an EAM driving apparatus of a related art is described below with reference to FIGS.1A through 1C. The EAM driving apparatus comprises a laser diode device (this is referred to as "LD device" hereinafter) 1, a modulation device 2, EAM 3, a reference voltage terminal 4, a bias terminal 5, and a driving terminal 6. The LD device 1 provides a LD device output 7 to the modulation device 2, and the modulation device 2 provides a modulation device output 8.
An input-output characteristic of the modulation device 2 is described below with reference to FIGS.2A through 2C. As is apparent from a curve (C) of FIG.2A, the light transmittance is approximately 100 % when the absolute value of the driving voltage (negative voltage) applied to the terminal 6 is zero (0) (point (C1)), most of light of the LD device output 7 applied to the modulation device 2 passes through modulation device 2, and appears as modulation device output 8 without experiencing significant attenuation. The LD device output 7 begins to be absorbed by the modulation device 2 at the point (C2) wherein the absolute value of the negative driving voltage begins to increase. Finally all of the LD device output 7 is absorbed by the modulation device 2 so that the modulation device output 8 is zero( 0 ), that is, the light is off, at the point (C3) when the absolute value of the negative driving voltage becomes equal to a predetermined value.
Therefore, an electrical driving waveform (in the negative driving voltage applied to the modulation device 2 ) such as shown in FIG.2B results in an optical output waveform (in the modulation device output 8) such as shown in FIG.2C in a case where the LD device output 7 supplied to the modulation device 2 is kept at a constant value.
There may be a case where the driving voltage applied to the modulation device 2 fluctuates in a range a delta-VH at the upper voltage (that is, small absolute value of a negative voltage) part of the driving waveform shown FIG.3B. Such fluctuation may occur because of, for example, the high harmonics present in such a pulse wave. In the above mentioned case, the optical output (modulation device output 8) fluctuates in the range delta-PH in the upper part of the optical output waveform shown in FIG.3C. Especially, as is shown in the curve (C), since the inclination of the curve (C) is sharp, the variation of the driving voltage is relatively amplified as a result of being converted into an optical output, in the upper part (C4). Thus, signal degradation occurs such as when a slight amount of ringing in an electrical driving waveform results in much noise appearing in the upper part of the optical output. This results in a degradation of parameters such as optical receiver code-error rate and optical waveform.
Therefore, in a long-distance optical transmission system, the EAM driving apparatus in the related art has a problem in that it is not possible to utilize the advantages of an optical fiber transmission line sufficiently, which advantages are obtained as a result of its low-loss and wide-frequency-range characteristics.
SUMMARY OF THE INVENTION
A general object of the present invention is to provide EAM driving apparatus and method wherein the above mentioned problem occurring in the related art is eliminated. A particular object of the present invention is to provide an EAM driving apparatus and method wherein signal fluctuation present in an input information signal does not result in noise in the optical output of the modulation device of the EAM.
According to one aspect of the invention there is provided an electric field absorption light modulation unit comprising a light emission device for emitting light; a modulation device for transmitting the light with a variable transmittance in order to provide modulated light; and driving signal generating means for generating in response to an input information signal a driving signal to be applied to the modulation device, the modulation device varying its light transmittance in response to the driving signal level, characterised in that the driving signal generating means has a level setting means setting the level of a portion of the driving signal in which an undesirable level fluctuation occurs to correspond to a constant working range of the modulation device, the light transmittance of the modulation device having a constant value in the constant working range.
According to another aspect of the invention an electric field absorption light modulation driving method is provided, comprising the steps of (a) causing a light emission device to emit light, (b) causing a modulation device to vary its light transmittance of light applied by the light emission device so as to provide light as a result of modifying thereof; and (c) generating a driving signal from an input information signal and applying the driving signal to the modulation device to vary the light transmittance thereof, in which step (c) provides a portion of the driving signal in which an undesirable level fluctuation occurs in a constant working range of the modulation device, the light transmittance of the modulation device staying at a constant value in the constant working range.
In the above mentioned configuration, said driving signal in a fluctuation range in which an undesirable level fluctuation may be present, corresponds to a constant working range of said modulation device, said light transmittance thereof staying at a constant value in said constant working range. Thus, the undesirable fluctuation present in the input information signal does not result in any noise appearing at the optical output. Therefore, for a long-distance optical transmission system, for example in an EAM driving apparatus using the above mentioned electric field light absorption modulation driving apparatus or method, it is possible to utilize the advantage of an optical fiber transmission line sufficiently, which advantages are obtained as a result of low-loss and wide-frequency-range characteristics.
Other objects and further features of the present invention will be more apparent from the following detailed description when read in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
  • FIGS.1A through 1C show diagrams of an EAM driving apparatus of the related art and relevant waveforms;
  • FIGS.2A through 2C show diagrams of input-output characteristics of a modulation device in the related art and relevant waveforms;
  • FIGS.3A through 3C show diagrams of input-output characteristics of a modulation device in the related art and relevant waveforms including an undesirable fluctuation;
  • FIGS.4A through 4D show diagrams of the principle illustration for an EAM driving apparatus of one embodiment according to the present invention and relevant waveforms;
  • FIGS.5A through 5C show diagrams of input-output characteristics of a modulation device in the EAM driving apparatus of one embodiment according to the present invention and relevant waveforms; and
  • FIGS.6A through 6D show diagrams of an EAM driving apparatus of one embodiment according to the present invention and relevant waveforms.
    • DESCRIPTION OF THE PREFERRED EMBODIMENT
    A principle of an EAM driving apparatus of one embodiment of an electrical field absorption light modulation driving apparatus and method according to the present invention is described below with reference to FIGS.4A through 4D. The configuration shown in FIG.4A resulted from modifying the configuration shown in FIG.1A. That is, an amplifying device 10 and modifying device 11 are added. Thus the description of those parts in the configuration in FIG.4A which correspond to the parts in FIG.1A is omitted, and the same numbers as those used for the parts in FIG.1A are given to the corresponding parts in FIG.4A.
    A predetermined voltage is applied to a terminal 4 of the EAM 3 so that the predetermined voltage is applied to the cathodes of both the LD device 1 and the modulation device 2, and a predetermined electric current IB is supplied to the anode of the LD device 1 via a terminal 5 of the EAM 3 so that the LD device 1 emits a constant light quantity, as shown in FIG.4A. Further, the anode of the modulation device 2 is connected to the output terminal of the modifying device 11 via a terminal 6 of the EAM 3, and the input terminal of the modifying device 11 is connected to the output terminal of the amplifying device.
    The modifying device 11 or both the amplifying device and the modifying device 11 acts or act as a driving signal generating means.
    An input information signal (input data as shown in FIG.4D) supplied to the input terminal 9 of the amplifying device 10 is then amplified and inverted in the amplifying device 10. The output signal of the amplifying device 10 is then supplied to the modifying device 11. The modifying device 11 then performs the following operation on the output signal of the device 10. The upper part of the electrical driving waveform (driving voltage, acting as a driving signal) is set to a constant non-zero voltage VH, as shown in FIGS.5A through 5C. The constant voltage VH in the present invention is obtained as a result of shifting the prior art constant voltage VH from zero (0) in a positive direction (left direction in FIGS.5A and 5B). The range between zero (0) voltage and the constant voltage VH is larger than the range obtained as a result of adding a predetermined margin range delta-VM to the range delta-VH of the expected undesirable fluctuation appearing in the H (high) level range (upper part) of the driving voltage as shown in FIGS.5A and 5B. The predetermined margin range delta-VM is determined as the result of consideration of each relevant component used, the range of ambient temperature at which the components are used, and various factors due to aging of the components.
    As is apparent from the portion (C6) of a curve (C5) of the driving voltage versus light transmittance of the modulation device 2 shown in FIG.5A, the light transmittance of the modulation device 2 is kept at a constant value (in this embodiment, this is 100 %) where a driving voltage is positive, that is, the characteristic curve (C5) has a saturation characteristic. Thus, in this range where the driving voltage is positive, the optical output is kept at a constant value in spite of any undesirable fluctuation being present in the driving voltage, under conditions where the light output applied to the modification device 2, which output is emitted from the LD device 1, is kept at a constant value.
    Therefore, the range delta-PH of the level fluctuation in the optical output is zero (0) as shown by FIG.5C even if a range delta-VH of voltage fluctuation is present in the driving voltage as shown in FIG.5B.
    That is, for example, the voltage fluctuation in a range delta-VH shown in FIG.3B being included in the electrical driving waveform does not result in the degradation shown in FIG.3C of the optical output waveform. The voltage fluctuation in the range delta-VH results from a corresponding level fluctuation being present in the input information signal (input data) supplied to the amplifying device 10. Thus, there results in no degradation of the light receiver code-error rate.
    A configuration of the EAM driving apparatus of the embodiment of electrical field absorption light modulation driving apparatus and method according to the present invention is described below with reference to FIGS.6A through 6D. The configuration in FIG.6A shows concrete forms of the amplifying device 10 and modifying device 11 shown in FIG.4A. Thus the description of those parts in FIG.6A which correspond to the parts in FIG.4A is omitted, and the same numbers as those used for the parts in FIG.4A are given to the corresponding parts in FIG.6A. The terminal 4 of the EAM, that is, the cathodes of both the LD device 1 and the modulation device 2, is grounded in this configuration as shown in FIG.6A.
    A transistor 20 (acting as an active element and being as a first pn junction element) acts to amplify and invert an input data waveform. A diode (being as a second pn junction element) 21 acts to modify the waveform, that is, to shift the level of the waveform, and a load resistor (acting as a load element) acts as load for the transistor 20. The diode 21 acts as a constant voltage providing means.
    A voltage VG corresponding to an input information signal (input data) is supplied to the gate of the transistor 20, a negative voltage VS is applied to a source of the transistor 20, and a voltage VD at the drain of the transistor 20 is applied to the terminal 6 of the EAM, that is, to the anode of the modulation device 2. The anode of the diode 21 is connected to the terminal 6 of the EAM 3, and a positive first reference voltage VR1 is applied to the cathode (24) of the diode 21. One terminal of the resistor 22 is connected to the terminal 6 of the EAM 3, and a positive second reference voltage VR2 is applied to the other terminal of the resistor 22.
    The operation of the transistor 20, the diode 21 and resistor 22 are described below.
    The transistor turns "ON" when the level of the input information signal (input data) goes high (H). Thus, the output voltage VD of the transistor 20 goes low. The present voltage VD is previously set to a voltage VL which is the negative bias voltage of the EAM 3, that is, which voltage causes the light transmittance of the modulation device 2 to be zero (0) % as shown in FIG.5A. Thus, the optical output of the modulation device of the EAM 3 is "OFF", that is, L (low) level shown FIG.6C when the level of the input information signal (input data) is H (high) level shown in FIG.6D.
    The transistor 20 turns "OFF" when the level of the input information signal (input data) is L (low). Then, the voltage at the anode (6) of the modulation device 2 becomes a constant value which is determined by the first and second reference voltages VR1 and VR2, characteristics of the diode 21, and the resistance value of the resistor 22. The present constant value is previously set to the above mentioned positive constant voltage VH shown in FIG.5A.
    The H (high) level range of the driving voltage corresponds to a range of the light transmittance of the modulation device 2, in which range the light transmittance is in a saturated condition. Thus, an optical output waveform should not contain noise, that is, the level fluctuation delta-PH appearing in the H (high) level range should be zero (0) as shown in FIG.5C.
    An advantage of the present invention is described below. As a result of the above mentioned operation for the embodiment according to the present invention, the level fluctuation, corresponding to the undesirable level fluctuation occurring in a driving voltage applied to the modulation device, appearing in the H level range of an optical output is suppressed even if the undesirable level fluctuation occurs in the H level range of the driving voltage. Thus, occurrence of noise in the H level range of the optical output, which occurrence results from slight degradation such as ringing in the electrical driving waveform is prevented. This results in prevention of degradation of the light receiver code-error rate and of the optical waveform. Therefore, it is possible to utilize the advantage of an optical fiber transmission line sufficiently, which advantage is obtained as a result of low-loss and wide-frequency-range characteristics.
    Further, the present invention is not limited to the above mentioned embodiments, and variations and modifications may be made without departing from the scope of the present invention.

    Claims (18)

    1. An electric field absorption light modulation unit (3) comprising
      a light emission device (1) for emitting light (7);
      a modulation device (2) for transmitting the light with a variable transmittance in order to provide modulated light (8); and
      driving signal generating means (10 and 11) for generating in response to an input information signal a driving signal to be applied to the modulation device (2), the modulation device (2) varying its light transmittance in response to the driving signal level,
         characterised in that the driving signal generating means (10 and 11) has a level-setting means (21) adapted to set the level of a portion of the driving signal in which an undesirable level fluctuation occurs to correspond to a constant working range of the modulation device (2), the light transmittance of the modulation device having a constant value in the constant working range.
    2. An apparatus according to claim 1, in which the level-setting means sets the driving signal to a level such that a predetermined margin range (ΔVm) in addition to the fluctuation (ΔVH) around the predetermined level corresponds to the constant working range of the modulation device.
    3. An apparatus according to any preceding claim, in which the modulation device has a maximum light transmittance in the said constant working range.
    4. An apparatus according to any preceding claim, in which the driving signal has a positive range and a negative range, the positive range including the said portion of the driving signal, and the negative range corresponding to a variation working range of the modulation device in which the light transmittance of the modulation device varies in response to a variation of the driving signal.
    5. An apparatus according to any preceding claim, in which the driving signal generating means further comprises amplifying means (20), coupled with the level setting means (21), for amplifying the input information signal, inverting the input information signal, and providing the amplified and inverted input information signal to the level setting means.
    6. An apparatus according to claim 5, in which the amplifying means comprises an active element (21) having an input terminal (9) at which the input information signal is applied, an output terminal connected to the modulation device and a bias terminal at which a bias voltage is applied, the active element connecting the output terminal and the bias terminal to each other when a predetermined first level of the input information signal is applied to the input terminal thereof so as to provide the driving signal to the modulation device, the output voltage being the same as the bias voltage, and the active element disconnecting the output terminal from the bias terminal when a predetermined second level of the input information signal is applied to the input terminal.
    7. An apparatus according to claim 6, in which the active element has a pn-junction element having a gate acting as the input terminal, a source acting as the output terminal, and a drain acting as the bias terminal.
    8. An apparatus according to claim 6 or 7, in which the amplifying means further comprises a load element connected to the output terminal of the active element for generating a predetermined voltage therein when electric current flows through the load element while the out terminal and the bias terminal of the active element are connected and the electric current flows through the active element.
    9. An apparatus according to any preceding claim, in which the level-setting means comprises a constant voltage providing means (21) for providing a constant voltage to the modulation device (2) so as to make the said portion of the driving signal in which the level fluctuation occurs correspond to the constant working range of the modulation device when the output terminal of the active element is disconnected from the bias terminal.
    10. An apparatus according to claim 9, in which the constant voltage providing means comprises a unidirectional current-flow device (21) having an anode and a cathode for allowing current to flow in a direction from the anode to the cathode when a voltage higher than another voltage applied to the cathode is applied to the anode, the said constant voltage being applied to the cathode of the unidirectional device and the anode of this device being connected to the modulation device.
    11. An apparatus according to claim 10, in which the unidirectional current-flow device has a pn-junction element.
    12. An apparatus according to any preceding claim, in which:
      the light emission device (1) and the modulation device (2) have anodes and cathodes, and the cathode of the light emission device is connected to the cathode of the modulation device; and
      the driving signal generating means comprises a first pn-junction element (20) having a gate, a source, and a drain, and a second pn-junction element (21) having an anode and a cathode, the input information signal being supplied to the gate of the first pn-junction element, a bias voltage being applied to the source of the first pn-junction element, the anode of the modulation device (2) being connected to the drain of the first pn-junction element and to the anode of the second pn-junction element, and a first reference voltage (VR1) being supplied to the cathode of the second pn-junction element.
    13. An apparatus according to claim 12, in which the driving signal generating means comprises a load element (21) for the first pn-junction element (20), the anode of the second pn-junction element (21) being connected with one terminal of the load element, and a second reference voltage (VR2) being applied to another terminal of the load element.
    14. An electric field absorption light modulation driving method using the steps of:
      (a) causing a light emission device (1) to emit light towards a modulation device (2);
      (b) causing the modulation device (2) to vary its transmittance of the light applied by the light emission device so as to provide modulated light; and
      (c) generating a driving signal from an input information signal and applying the driving signal to the modulation device to vary its light transmittance;
         characterised in that step (c) sets the level of a portion of the driving signal in which an undesirable level fluctuation occurs to correspond to a constant working range of the modulation device, the light transmittance of the modulation device staying at a constant value in this constant working range.
    15. An electric field absorption light modulation driving method according to claim 14, in which step (c) sets the voltage of the said portion of the driving signal to a level such that a margin around the voltage fluctuation is within the constant working range.
    16. An electric field absorption light modulation driving method according to claim 14 or 15, in which the modulation device has a maximum light transmittance in the constant working range.
    17. An electric field absorption light modulation driving method according to any of claims 14-16, in which the driving signal has a positive range and a negative range, the positive range including the said portion of the driving voltage, and the negative range corresponding to a range of the modulation device in which the light transmittance of the modulation device varies in response to a variation of the driving signal.
    18. An electric field absorption light modulation driving method according to any of claims 14-17, in which step (b) further comprises the steps of amplifying the input information signal, then inverting the input information signal, and then providing the amplified and inverted input information signal to a level-setting means.
    EP92309917A 1991-10-31 1992-10-29 Electric field absorption light modulation driving apparatus and method Expired - Lifetime EP0540331B1 (en)

    Applications Claiming Priority (2)

    Application Number Priority Date Filing Date Title
    JP286142/91 1991-10-31
    JP3286142A JP3008608B2 (en) 1991-10-31 1991-10-31 Electroabsorption type optical modulator driving method

    Publications (3)

    Publication Number Publication Date
    EP0540331A2 EP0540331A2 (en) 1993-05-05
    EP0540331A3 EP0540331A3 (en) 1993-09-01
    EP0540331B1 true EP0540331B1 (en) 1998-01-07

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    Family Applications (1)

    Application Number Title Priority Date Filing Date
    EP92309917A Expired - Lifetime EP0540331B1 (en) 1991-10-31 1992-10-29 Electric field absorption light modulation driving apparatus and method

    Country Status (4)

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    US (1) US5317581A (en)
    EP (1) EP0540331B1 (en)
    JP (1) JP3008608B2 (en)
    DE (1) DE69223923T2 (en)

    Families Citing this family (10)

    * Cited by examiner, † Cited by third party
    Publication number Priority date Publication date Assignee Title
    EP0984534B1 (en) * 1994-03-18 2003-06-04 Fujitsu Limited Drive circuit of a semiconductor optical modulator
    US5483186A (en) * 1994-05-05 1996-01-09 At&T Corp. Push-pull optical modulator driver circuit
    US5521738A (en) * 1994-06-30 1996-05-28 At&T Corp. Data encoded optical pulse generator
    US5488503A (en) * 1995-02-09 1996-01-30 Hughes Aircraft Company Low-power, stabilized, photonic modulator system
    JP3553222B2 (en) * 1995-09-20 2004-08-11 三菱電機株式会社 Optical modulator module
    FR2740285B1 (en) * 1995-10-23 1997-11-21 Alcatel Submarcom AMPLITUDE MODULATION DEVICE WITH ELECTRO ABSORPTION MODULATOR
    JP3816648B2 (en) * 1997-10-14 2006-08-30 富士通株式会社 Drive circuit for electroabsorption optical modulator
    US5882106A (en) * 1997-12-10 1999-03-16 Galli; Robert Thin profile laser pointer assembly
    JP4046535B2 (en) * 2002-03-29 2008-02-13 ユーディナデバイス株式会社 Optical semiconductor device, optical module, and optical semiconductor drive circuit
    JP7430479B2 (en) * 2017-12-18 2024-02-13 日本ルメンタム株式会社 Optical transmission subassembly and optical module

    Family Cites Families (2)

    * Cited by examiner, † Cited by third party
    Publication number Priority date Publication date Assignee Title
    JPS5552022A (en) * 1978-10-13 1980-04-16 Matsushita Electric Ind Co Ltd Light modulating device
    US5208817A (en) * 1992-04-10 1993-05-04 At&T Bell Laboratories Modulator-based lightwave transmitter

    Also Published As

    Publication number Publication date
    US5317581A (en) 1994-05-31
    DE69223923D1 (en) 1998-02-12
    EP0540331A2 (en) 1993-05-05
    JPH05129697A (en) 1993-05-25
    JP3008608B2 (en) 2000-02-14
    EP0540331A3 (en) 1993-09-01
    DE69223923T2 (en) 1998-04-30

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